Plants having increased yield and method for making the same

ABSTRACT

The present invention concerns a method for increasing plant yield in plants grown under non-stress growth conditions relative to yield in corresponding wild type plants grown under comparable conditions, the method comprising preferentially increasing activity in the cytosol of a plant cell of a type I DnaJ-like polypeptide or a homologue thereof. One such method comprises introducing and/or expressing in a plant, plant part or plant cell a type I DnaJ-like nucleic acid or variant thereof. The invention also relates to transgenic plants grown under non-stress conditions having introduced and/or expressed therein a type I DnaJ-like nucleic acid or variant thereof, which plants have increased plant yield relative to corresponding wild type plants grown under comparable conditions. The present invention also concerns constructs useful in the methods of the invention.

RELATED APPLICATIONS

This application is a national stage application (under 35 U.S.C. 371) of PCT/EP2005/057167 filed Dec. 23, 2005, which claims benefit of European application 04106985.7 filed Dec. 24, 2004 and U.S. Provisional Application 60/641,688 filed Jan. 6, 2005.

SUBMISSION OF SEQUENCE LISTING

The Sequence Listing associated with this application is filed in electronic format via EFS-Web and hereby incorporated by reference into the specification in its entirety. The name of the text file containing the Sequence Listing is Sequence_Listing_(—)14546_(—)00019. The size of the text file is 172 KB, and the text file was created on Jan. 4, 2010.

DnaJ domain proteins (or DnaJ proteins) of type I (to date there being at least 8 in Arabidopsis; Miernyk (2001) Cell Stress & Chaperone 6(3): 209-218), comprise (from amino terminus to carboxy terminus) the domains identified within the archetypal DnaJ protein as first characterized in Escherichia coli:

-   -   1) a G/F domain region of about 30 amino acid residues, rich in         glycine (G) and phenylalanine (F), which is proposed to regulate         target polypeptide specificity;     -   2) a Cys-rich zinc finger domain containing four repeats of the         CXXCXGXG (SEQ ID NO: 66), where X represents a charged or polar         residue; these four repeats function in pairs to form zinc         binding domain I and II (InterPro reference IPR001305; Linke et         al. (2003) J Biol Chem 278(45): 44457-44466); the zinc finger         domain is thought to mediate direct protein:protein interactions         and more specifically to bind non-native polypeptides to be         delivered to Hsp70;     -   3) a carboxy-terminal domain (CTD; InterPro reference         IPR002939).

The present invention relates generally to the field of molecular biology and concerns a method for increasing plant yield, in plants grown under non-stress conditions, relative to yield in corresponding wild type plants grown under comparable conditions. More specifically, the present invention concerns a method for increasing plant yield in plants grown under non-stress conditions, comprising preferentially increasing activity in the cytosol of a plant cell of a type I DnaJ-like polypeptide or a homologue thereof. The present invention also concerns plants having preferentially increased activity in the cytosol of a type I DnaJ-like polypeptide or a homologue thereof, which plants have increased yield when grown under non-stressed conditions relative to yield in corresponding wild type plants grown under comparable conditions. The invention also provides constructs useful in the methods of the invention.

The ever-increasing world population and the dwindling supply of arable land available for agriculture fuel agricultural research towards improving the efficiency of agriculture. Conventional means for crop and horticultural improvements utilise selective breeding techniques to identify plants having desirable characteristics. However, such selective breeding techniques have several drawbacks, namely that these techniques are typically labour intensive and result in plants that often contain heterogeneous genetic components that may not always result in the desirable trait being passed on from parent plants. Advances in molecular biology have allowed mankind to modify the germplasm of animals and plants. Genetic engineering of plants entails the isolation and manipulation of genetic material (typically in the form of DNA or RNA) and the subsequent introduction of that genetic material into a plant. Such technology has the capacity to deliver crops or plants having various improved economic, agronomic or horticultural traits. A trait of particular economic interest is yield. Yield is normally defined as the measurable produce of economic value from a crop. This may be defined in terms of quantity and/or quality. Yield is directly dependent on several factors, for example, the number and size of the organs, plant architecture (for example, the number of branches), seed production and more. Root development, nutrient uptake and stress tolerance may also be important factors in determining yield. Optimizing one of the abovementioned factors may therefore increase crop yield. Furthermore, plant seeds are an important source of human and animal nutrition. Crops such as, corn, rice, wheat, canola and soybean account for over half of total human caloric intake, whether through direct consumption of the seeds themselves or through consumption of meat products raised on processed seeds. They are also a source of sugars, oils and many kinds of metabolites used in industrial processes. Seeds contain an embryo, the source of new shoots and roots after germination, and an endosperm, the source of nutrients for embryo growth, during germination and early growth of seedlings. The development of a seed involves many genes, and requires the transfer of metabolites from roots, leaves and stems into the growing seed. The endosperm, in particular, assimilates the metabolic precursors of carbohydrate polymers, oil and proteins and synthesizes them into storage macromolecules to fill out the grain. The ability to increase plant seed yield, whether through increased harvest index, increased thousand kernel weight, seed number, seed biomass, seed development, seed filling or any other seed-related trait would have many applications in agriculture, and even many non-agricultural uses such as in the biotechnological production of substances such as pharmaceuticals, antibodies or vaccines.

It has now been found that preferentially increasing activity in the cytosol of a plant cell of a type I DnaJ-like polypeptide gives plants grown under non-stress conditions increased yield relative to corresponding wild type plants grown under comparable conditions.

DnaJ is a molecular co-chaperone of the Hsp40 (Heat shock protein 40) family. Hsp40 cooperates with chaperone heat shock protein 70 (Hsp70, also called DnaK) and co-chaperone nucleotide exchange factor GrpE to facilitate different aspects of cellular protein metabolism that include ribosome assembly, protein translocation, protein folding and unfolding, suppression of polypeptide aggregation and cell signalling (Walid (2001) Curr Protein Peptide Sci 2: 227-244). DnaJ stimulates Hsp70 to hydrolyze ATP, a key step in the stable binding of a substrate to Hsp70. In addition, DnaJ itself also possesses molecular chaperone functions since it has been shown to bind to nascent chains in in vitro translation systems and to prevent the aggregation of denatured polypeptides (Laufen et al. (2001) Proc Natl Acad Sci USA 96: 5452-5457). Members of the DnaJ family have been identified in a variety of organisms (both in prokaryotes and eucaryotes) and in a variety of cellular compartments, such as cytosol, mitochondria, peroxisome, glyoxysome, endoplasmic reticulum and chloroplast stroma. Within one organism, multiple Hsp40s can interact with a single Hsp70 to generate Hsp70::Hsp40 pairs that facilitate numerous reactions in cellular protein metabolism.

All DnaJ proteins are defined by the presence of a so-called “J” domain, consisting of approximately 70 amino acids, usually located at the amino terminus of the protein, and by the presence of the highly conserved HPD tri-peptide in the middle of the J-domain (InterPro reference IPR001623; Zdobnov et al., (2002) 18(8): 1149-50); The “J” domain, consisting of four alpha helices, interacts with Hsp70 proteins. In the genome of Arabidopsis thaliana, at least 89 proteins comprising the J-domain have been identified (Miernyk (2001) Cell Stress & Chaperones). 18 Hsp70 proteins have been identified to date.

DnaJ proteins have been further classified into Type I, Type II and Type III.

DnaJ domain proteins (or DnaJ proteins) of type I (to date there being at least 8 in Arabidopsis; Miernyk (2001) Cell Stress & Chaperone 6(3): 209-218), comprise (from amino terminus to carboxy terminus) the domains identified within the archetypal DnaJ protein as first characterized in Escherichia coli:

-   -   1) a G/F domain region of about 30 amino acid residues, rich in         glycine (G) and phenylalanine (F), which is proposed to regulate         target polypeptide specificity;     -   2) a Cys-rich zinc finger domain containing four repeats of the         CXXCXGXG, where X represents a charged or polar residue; these         four repeats function in pairs to form zinc binding domain I and         II (InterPro reference IPR001305; Linke et al. (2003) J Biol         Chem 278(45): 44457-44466); the zinc finger domain is thought to         mediate direct protein:protein interactions and more         specifically to bind non-native polypeptides to be delivered to         Hsp70;     -   3) a carboxy-terminal domain (CTD; InterPro reference         IPR002939).

Type II DnaJ domain proteins (to date there being at least 35 in Arabidopsis) comprise the J domain located at the amino terminus of the protein, either the G/F domain or the zinc finger domain and a CTD. Type III DnaJ domain proteins (to date there being at least 45 in Arabidopsis) comprise only the J domain, which may be located anywhere within the protein.

In their native form, DnaJ proteins may be targeted to a variety of subcellular compartments, in either a soluble or a membrane-bound form. Examples of such subcellular compartments in plants include mitochondria, chloroplasts, peroxisomes, nucleus, cytoplasm and secretory pathway. Signal sequences and transit peptides, usually located at the amino terminus of the nuclear-encoded DnaJ proteins, are responsible for the targeting of these proteins to specific subcellular compartments.

Examples of cellular membranes to which DnaJ proteins may be targeted under specific circumstances include the mitochondrial outer membrane, the chloroplastic outer membrane, the peroxisomal membrane, the nuclear envelope, the endoplasmic reticulum (ER) and the cell membrane itself (Miernyk (2001) Cell Stress & Chaperone 6(3): 209-218). One type of membrane association of a DnaJ protein happens after posttranslational modification of the protein, i.e., after isoprenylation. An isoprenoid group is attached to the cysteine of the farnesylation CaaX motif (where C is Cys, a an aliphatic amino acid residue and X any amino acid) located at the carboxy terminus end of the protein. This farnesylation has been shown to result in higher biological activity and membrane association of the DnaJ protein, especially at elevated temperatures (Zhu J-K et al., (1993) The Plant Cell 5:341-9).

It has been suggested that DnaJ proteins play a role (together with HSP70) in conferring tolerance to heat stress in plants. Whilst DnaJ may have a protective role to play in heat-stressed plants, it is not apparent whether there might be any added advantage to increasing levels and/or activity of DnaJ in nonheat-stressed plants.

It was therefore surprising to find that a type I DnaJ-like polypeptide could be used under non-stress growth conditions to give plants having increased yield relative to yield in corresponding wild type plants grown under comparable conditions.

Therefore, according to one embodiment of the present invention, there is provided a method for increasing plant yield in plants grown under non-stress conditions, comprising preferentially increasing activity in the cytosol of a plant cell of a type I DnaJ-like polypeptide or a homologue thereof, which type I DnaJ-like polypeptide or homologue thereof comprises a CaaX motif in its carboxy terminus.

The term “cytosol” refers to the subcellular location of the DnaJ protein useful in the methods of the invention. A transient or prolonged association of the DnaJ protein with the outer surface of mitochondria, chloroplasts, peroxisome, nucleus, ER or with the cellular membrane, is encompassed by the term cytosol.

The “carboxy terminus” of a protein may readily be identified by a person skilled in the art.

Reference herein to “corresponding wild type plants” is taken to mean any suitable control plant or plants, the choice of which would be within the capabilities of a person skilled in the art and may include, for example, corresponding wild type plants or corresponding plants without the gene of interest. A “control plant” as used herein refers not only to whole plants, but also to plant parts, including seeds and seed parts.

Reference herein to “non-stressed (growth) conditions” is taken to mean growth/cultivation of a plant at any stage in its life cycle (from seed to mature plant and back to seed again) under normal growth conditions, which include the everyday mild stresses that every plant encounters, but which do not include severe stress. An example of a severe stress is heat stress, the occurrence of which would be well known in the art, and which would depend upon various factors, such as the region in which the plant is grown and which would depend upon the plant itself.

Advantageously, performance of the methods according to the present invention results in plants having increased plant yield, particularly increased seed yield.

The term “increased yield” as defined herein is taken to mean an increase in any one or more of the following, each relative to corresponding wild type plants: (i) increased biomass (weight) of one or more parts of a plant, particularly aboveground (harvestable) parts, increased root biomass or increased biomass of any other harvestable part; (ii) increased seed yield, which includes an increase in seed biomass (seed weight) and which may be an increase in the seed weight per plant or on an individual seed basis; (iii) increased number of (filled) seeds; (iv) increased fill rate (which is the number of filled seeds divided by the total number of seeds and multiplied by 100); (v) increased seed size, which may also influence the composition of seeds; (vi) increased seed volume, which may also influence the composition of seeds; (vii) increased harvest index, which is expressed as a ratio of the yield of harvestable parts, such as seeds, over the total biomass; and (viii) increased thousand kernel weight (TKW), which is extrapolated from the number of filled seeds counted and their total weight. An increased TKW may result from an increased seed size and/or seed weight.

Taking corn as an example, a yield increase may be manifested as one or more of the following: increase in the number of plants per hectare or acre, an increase in the number of ears per plant, an increase in the number of rows, number of kernels per row, kernel weight, thousand kernel weight, ear length/diameter, among others. Taking rice as an example, a yield increase may be manifested as an increase in one or more of the following: number of plants per hectare or acre, number of panicles per plant, number of spikelets per panicle, number of flowers per panicle, increase in the seed filling rate, increase in thousand kernel weight, among others. An increase in yield may also result in modified architecture, or may occur because of modified architecture.

According to a preferred feature, performance of the methods of the invention result in plants having increased seed yield. Therefore, according to the present invention, there is provided a method for increasing plant seed yield in plants grown under non-stress conditions, which method comprises preferentially increasing activity in the cytosol of a plant cell of a type I DnaJ-like polypeptide or a homologue thereof, which type I DnaJ-like polypeptide comprises a CaaX motif at its carboxy terminus.

Further preferably, the increased seed yield is manifested as an increase in harvest index relative to corresponding wild type plants. Therefore, according to the present invention, there is provided a method for increasing harvest index in plants grown under non-stress conditions, which method comprises preferentially increasing activity in the cytosol of a plant cell of a type I DnaJ-like polypeptide or a homologue thereof, which type I DnaJ-like polypeptide comprises a CaaX motif at its carboxy terminus.

Since the transgenic plants according to the present invention have increased yield, it is likely that these plants exhibit an increased growth rate (during at least part of their life cycle), relative to the growth rate of corresponding wild type plants at a corresponding stage in their life cycle. The increased growth rate may be specific to one or more parts of a plant (including seeds), or may be throughout substantially the whole plant. A plant having an increased growth rate may even exhibit early flowering. The increase in growth rate may take place at one or more stages in the life cycle of a plant or during substantially the whole plant life cycle. Increased growth rate during the early stages in the life cycle of a plant may reflect enhanced vigour. The increase in growth rate may alter the harvest cycle of a plant allowing plants to be sown later and/or harvested sooner than world otherwise be possible. If the growth rate is sufficiently increased, it may allow for the further sowing of seeds of the same plant species (for example sowing and harvesting of rice plants followed by sowing and harvesting of further rice plants all within one conventional growing period). Similarly, if the growth rate is sufficiently increased, it may allow for the further sowing of seeds of different plants species (for example the sowing and harvesting of rice plants followed by, for example, the sowing and optional harvesting of soybean, potato or any other suitable plant crop). Harvesting additional times from the same rootstock in the case of some plants may also be possible. Altering the harvest cycle of a plant may lead to an increase in annual biomass production per acre (due to an increase in the number of times (say in a year) that any particular plant may be grown and harvested). An increase in growth rate may also allow for the cultivation of transgenic plants in a wider geographical area than their wild-type counterparts, since the territorial limitations for growing a crop are often determined by adverse environmental conditions either at the time of planting (early season) or at the time of harvesting (late season). Such adverse conditions may be avoided if the harvest cycle is shortened. The growth rate may be determined by deriving various parameters from growth curves, such parameters may be: T-Mid (the time taken for plants to reach 50% of their maximal size) and T-90 (time taken for plants to reach 90% of their maximal size), amongst others.

Performance of the methods of the invention gives plants having an increased growth rate. Therefore, according to the present invention, there is provided a method for increasing the growth rate of plants grown under non-stress conditions relative to the growth rate of wild type plants grown under comparable conditions, which method comprises preferentially increasing activity in the cytosol of a plant cell of a type I DnaJ-like polypeptide or a homologue thereof, which type I DnaJ-like polypeptide or homologue thereof comprises a CaaX motif at its carboxy terminus.

The abovementioned growth characteristics may advantageously be modified in any plant.

The term “plant” as used herein encompasses whole plants, ancestors and progeny of the plants and plant parts, including seeds, shoots, stems, leaves, roots (including tubers), flowers, and tissues and organs, wherein each of the aforementioned comprise the gene/nucleic acid of interest. The term “plant” also encompasses plant cells, suspension cultures, callus tissue, embryos, meristematic regions, gametophytes, sporophytes, pollen, and microspores, again wherein each of the aforementioned comprise the gene/nucleic acid of interest.

Plants that are particularly useful in the methods of the invention include all plants which belong to the superfamily Viridiplantae, in particular monocotyledonous and dicotyledonous plants including fodder or forage legumes, ornamental plants, food crops, trees or shrubs selected from the list comprising Acacia spp., Acer spp., Actinidia spp., Aesculus spp., Agathis australis, Albizia amara, Alsophila tricolor, Andropogon spp., Arachis spp, Areca catechu, Astelia fragrans, Astragalus cicer, Baikiaea plunjuga, Betula spp., Brassica spp., Bruguiera gymnorrhiza, Burkea africana, Butea frondosa, Cadaba farinosa, Calliandra spp, Camellia sinensis, Canna indica, Capsicum spp., Cassia spp., Centroema pubescens, Chaenomeles spp., Cinnamomum cassia, Coffea arabica, Colophospermum mopane, Coronillia varia, Cotoneaster serotina, Crataegus spp., Cucumis spp., Cupressus spp., Cyathea dealbata, Cydonia oblonga, Cryptomeria japonica, Cymbopogon spp., Cynthea dealbata, Cydonia oblonga, Dalbergia monetaria, Davallia divaricata, Desmodium spp., Dicksonia squarosa, Diheteropogon amplectens, Dioclea spp, Dolichos spp., Dorycnium rectum, Echinochloa pyramidalis, Ehrartia spp., Eleusine coracana, Eragrestis spp., Erythrina spp., Eucalyptus spp., Euclea schimperi, Eulalia villosa, Fagopyrum spp., Feijoa sellowiana, Fragaria spp., Flemingia spp, Freycinetia banksii, Geranium thunbergii, Ginkgo biloba, Glycine javanica, Gliricidia spp, Gossypium hirsutum, Grevillea spp., Guibourtia coleosperma, Hedysarum spp., Hemarthia altissima, Heteropogon contortus, Hordeum vulgare, Hyparrhenia rufa, Hypericum erectum, Hyperthelia dissoluta, Indigo incamata, Iris spp., Leptarrhena pyrolifolia, Lespediza spp., Leffuca spp., Leucaena leucocephala, Loudetia simplex, Lotonus bainesii, Lotus spp., Macrotyloma axillare, Malus spp., Manihot esculenta, Medicago sauva, Metasequoia glyptostroboides, Musa sapientum, Nicotianum spp., Onobrychis spp., Ornithopus spp., Oryza spp., Peltophorum africanum, Pennisetum spp., Persea gratissima, Petunia spp., Phaseolus spp., Phoenix canariensis, Phonnium cookianum, Photinia spp., Picea glauca, Pinus spp., Pisum sativum, Podocarpus totara, Pogonarthria fleckii, Pogonarthria squarrosa, Populus spp., Prosopis cineraria, Pseudotsuga menziesii, Pterolobium stellatum, Pyrus communis, Quercus spp., Rhaphiolepsis umbellata, Rhopalostylis sapida, Rhus natalensis, Ribes grossularia, Ribes spp., Robinia pseudoacacia, Rosa spp., Rubus spp., Salix spp., Schyzachyrium sanguineum, Sciadopitys verticillata, Sequoia sempervirens, Sequoiadendron giganteum, Sorghum bicolor, Spinacia spp., Sporobolus fimbriatus, Stiburus alopecuroides, Stylosanthos humilis, Tadehagi spp, Taxodium distichum, Themeda triandra, Trifolium spp., Triticum spp., Tsuga heterophylla, Vaccinium spp., Vicia spp., Vitis vinifera, Watsonia pyramidata, Zantedeschia aethiopica, Zea mays, amaranth, artichoke, asparagus, broccoli, Brussels sprouts, cabbage, canola, carrot, cauliflower, celery, collard greens, flax, kale, lentil, oilseed rape, okra, onion, potato, rice, soybean, strawberry, sugar beet, sugarcane, sunflower, tomato, squash, tea and algae, amongst others.

Preferably, the plant is a crop plant such as soybean, sunflower, canola, alfalfa, rapeseed, cotton, tomato, potato or tobacco. Further preferably, the plant is a monocotyledonous plant, such as sugarcane. More preferably the plant is a cereal, such as rice, maize, wheat, barley, millet, rye, sorghum or oats.

The activity of a type I DnaJ-like polypeptide may be increased by raising levels of the polypeptide. Alternatively, activity may also be increased when there is no change in levels of a type I DnaJ-like polypeptide, or even when there is a reduction in levels of a type I DnaJ-like polypeptide. This may occur when the intrinsic properties of the polypeptide are altered, for example, by making mutant versions that are more active that the wild type polypeptide. Reference herein to “preferentially” increasing activity is taken to mean a targeted increase in activity of a type I DnaJ-like polypeptide or a homologue thereof in the cytosol of a plant grown under non-stressed conditions, which increase in activity is above that found in the cytosol of cells of wild type plants grown under comparable conditions.

The term “type I DnaJ-like polypeptide or a homologue thereof” as defined herein refers to a type I DnaJ polypeptide comprising a CaaX motif at its carboxy terminus.

Common to all DnaJ proteins is the presence of a J-domain, which consists of approximately 70 amino acids (usually located at the amino terminus of the protein) and which comprises the highly conserved HPD tri-peptide in its middle (InterPro reference IPR001623; Zdobnov et al., (2002) 18(8): 1149-50); The “J” domain, consisting of four alpha helices, interacts with Hsp70 proteins. In the genome of Arabidopsis thaliana, at least 89 proteins comprising the J-domain have been identified (Miernyk (2001) Cell Stress & Chaperones). To date, 18 Hsp70 proteins have been identified.

Type I DnaJ domain proteins (or DnaJ proteins) are further characterised by the presence of the following from amino terminus to carboxy terminus:

1. a G/F domain region of about 30 amino acid residues, rich in glycine (G) and phenylalanine (F), which is proposed to regulate target polypeptide specificity; and

2. a Cys-rich zinc finger domain containing four repeats of the CXXCXGXG(SEQ ID NO: 66), where X represents a charged or polar residue; these four repeats function in pairs to form zinc binding domain I and II (InterPro reference IPR001305; Linke et al. (2003) J Biol Chem 278(45): 44457-44466); the zinc finger domain is thought to mediate direct protein:protein interactions and more specifically to bind non-native polypeptides to be delivered to Hsp70; and

3. a carboxy-terminal domain (CTD; InterPro reference IPR002939).

In their native form, DnaJ proteins may be targeted to a variety of subcellular compartments, in either a soluble or a membrane-bound form. DnaJ proteins useful in methods of the invention are those without a signal sequence or a transit peptide, and are therefore principally located in the cytosol of a plant cell.

DnaJ proteins useful in methods of the invention are those comprising a CaaX motif at their carboxy terminus. This polypeptide is thus present in either a soluble or a membrane-bound form, with existence in either form being reversible.

A “type I DnaJ-like polypeptide or a homologue thereof” may readily be identified using routine techniques well known in the art. For example, stimulation of the ATPase activity of DnaK by DnaJ may readily be determined in vitro as in Zhou et al., (2000), Protein Expression & Purification 19: 253-258. The ability of DnaJ to promote complex formation between DnaK and non-native polypeptides, such as denatured luciferase, may be determined by ELISA (Fan et al., (2004) Molec. Biol. Cell 15: 761-773).

A “type I DnaJ-like polypeptide or a homologue thereof” may readily be identified using sequence alignment. Methods for the alignment of sequences for comparison are well known in the art, such methods include GAP, BESTFIT, BLAST, FASTA and TFASTA. GAP uses the algorithm of Needleman and Wunsch ((1970) J Mol Biol 48: 443-453) to find the alignment of two complete sequences that maximizes the number of matches and minimizes the number of gaps. The BLAST algorithm (Altschul et al., (1990) J Mol Biol 215: 403-10) calculates percent sequence identity and performs a statistical analysis of the similarity between the two sequences. The software for performing BLAST analysis is publicly available through the National Centre for Biotechnology Information. Homologues of type I DnaJ-like polypeptides and their percentage of identity to the type I DnaJ-like amino acid sequence useful in methods of the invention, as represented by SEQ ID NO: 2, may readily be identified using, for example, the VNTI AlignX multiple alignment program, based on a modified ClustalW algorithm (InforMax, Bethesda, Md., with default settings for gap opening penalty and gap extension. Preferably, type I DnaJ-like polypeptides or homologues thereof comprising a CaaX motif at their carboxy terminus, and which are useful in methods of the invention, are those having in increasing order of preference at least 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95% identity to SEQ ID NO: 2.

Examples of polypeptides covered by the term “type I DnaJ-like polypeptide or a homologue thereof” are listed in Table 1 as SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 18, SEQ ID NO: 20, SEQ ID NO: 22, SEQ ID NO: 24, SEQ ID NO: 26, SEQ ID NO: 28, SEQ ID NO: 30, SEQ ID NO: 32, SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54 and SEQ ID NO: 56. Type I DnaJ-like polypeptide sequence used to exemplify the invention is as represented by SEQ ID NO: 2.

TABLE 1 Examples of nucleic acids (DNA SEQ ID) from different organisms encoding type I DnaJ-like polypeptides (Protein SEQ ID) Accession Accession number number Protein SEQ Gene Name DNA DNA SEQ ID protein ID Source CDS1877 AK066420.1 SEQ ID NO: VT SEQ ID NO: Oryza sativa DnaJ 1 2 Orysa_DNAJ AK10195 SEQ ID NO: VT SEQ ID NO: Oryza sativa II CAAX 3 4 Orysa_DNAJ AK105028 SEQ ID NO: VT SEQ ID NO: Oryza sativa III CAAX 5 6 Orysa_DNAJ AK104315 SEQ ID NO: VT SEQ ID NO: Oryza sativa IV CAAX 7 8 Zeama_ZMDJ BT016805 * SEQ ID NO: T01643 SEQ ID NO: Zea mays 1 9 10 Zeama_DNAJ AY103727.1 SEQ ID NO: VT SEQ ID NO: Zea mays I CAAX 11 12 Zeama_DNAJ AY108160.1 SEQ ID NO: VT SEQ ID NO: Zea mays II CAAX 13 14 Triae_DNAJ BT008914.1 SEQ ID NO: VT SEQ ID NO: Triticum 15 16 aestivum At5g22060 L36113 SEQ ID NO: AAB8679 SEQ ID NO: Arabidopsis AtJ2 CAAX 17 18 thaliana At3g44110 NM_114279 SEQ ID NO: S71199 SEQ ID NO: Arabidopsis AtJ3 CAAX 19 20 thaliana Atrnu_DNAJ L09124 SEQ ID NO: VT SEQ ID NO: Atriplex 21 22 nummularia Cucsa_DNAJ- X67695 SEQ ID NO: VT SEQ ID NO: Cucumis 1 23 24 sativus Dauca_J1P AF308737 SEQ ID NO: VT SEQ ID NO: Daucus carota 25 26 Glyma_pm37 AF169022 SEQ ID NO: VT SEQ ID NO: Glycine max DNAJ 27 28 Hevbr_DNAJ AF085275 SEQ ID NO: AAD1205 SEQ ID NO: Hevea 29 30 brasiliensis Lyces_DNAJ AF124139 SEQ ID NO: AAF28382 SEQ ID NO: Lycopersicum 31 32 esculentum Medsa_DNAJ AJ000995 SEQ ID NO: CAA0444 SEQ ID NO: Medicago 33 34 sativa Nicta_DNAJ AJ299254 SEQ ID NO: CAC1282 SEQ ID NO: Nicotiana 35 36 tabacum Salgi_DNAJ2 AB003137 SEQ ID NO: BAA7688 SEQ ID NO: Salix gilgiana 37 38 Salgi_DNAJ AB015601 SEQ ID NO: BAA3512 SEQ ID NO: Salix gilgiana 39 40 Solto_DNAJ X94301 SEQ ID NO: CAA6396 SEQ ID NO: Solanum 41 42 tuberosum Orysa_DNAJ AK110691 SEQ ID NO: VT SEQ ID NO: Oryza sativa CASQ 43 44 Triae_DNAJ II BT009366 SEQ ID NO: VT SEQ ID NO: Triticum CASQ 45 46 aestivum Ceael_DNaJ NM_072051 SEQ ID NO: NP_50445 SEQ ID NO: Caenorhabditis 47 48 elegans Homsa_HsJ2 D13388 SEQ ID NO: P31689 SEQ ID NO: Homo sapiens 49 50 Sacce_YDJ1 NC_001146 SEQ ID NO: NP_01433 SEQ ID NO: Saccharomyces 51 52 cereviseae Homsa_DNAJ NM_005880 SEQ ID NO: NP_00587 SEQ ID NO: Homo sapiens A2 53 54 Musmu_mDj3 NM_019794 SEQ ID NO: Q9QYJ0 SEQ ID NO: Mus musculus 55 56 VT = virtual translation; * with minor corrections

It is to be understood that sequences falling under the definition of type I DnaJ-like polypeptide or homologue thereof are not to be limited to SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 18, SEQ ID NO: 20, SEQ ID NO: 22, SEQ ID NO: 24, SEQ ID NO: 26, SEQ ID NO: 28, SEQ ID NO: 30, SEQ ID NO: 32, SEQ ID NO: 34, SEQ ID NO: 36, SEQ ID NO: 38, SEQ ID NO: 40, SEQ ID NO: 42, SEQ ID NO: 44, SEQ ID NO: 46, SEQ ID NO: 48, SEQ ID NO: 50, SEQ ID NO: 52, SEQ ID NO: 54 and SEQ ID NO: 56 listed in Table 1, but that any type I DnaJ-like polypeptide comprising a CaaX motif at its carboxy terminus may be suitable for use in the methods of the invention.

The nucleic acid encoding a type I DnaJ-like polypeptide or a homologue thereof may be any natural or synthetic nucleic acid. Therefore the term “type I DnaJ-like nucleic acid/gene” as defined herein is any nucleic acid/gene encoding a type I DnaJ-like polypeptide or a homologue thereof as defined hereinabove. Examples of type I DnaJ-like nucleic acids include those listed in Table 1 as SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 19, SEQ ID NO: 21, SEQ ID NO: 23, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51 SEQ ID NO: 53 and SEQ ID NO: 55. Type I DnaJ-like nucleic acids/genes and variants thereof may be suitable in practising the methods of the invention. Variant type I DnaJ-like nucleic acid/genes include portions of a type I DnaJ-like nucleic acid/gene and/or nucleic acids capable of hybridising with a type I DnaJ-like nucleic acid/gene.

The term portion as defined herein refers to a piece of DNA comprising at least 600 nucleotides, which portion encodes a polypeptide of at least 200 amino acids, comprising from the amino terminus to the carboxy terminus, a DnaJ domain, a G/F rich domain and a Cys-rich zinc finger domain, a CTD domain and a CaaX motif. Preferably, the portion comprises at least 1050 nucleotides, which portion encodes a polypeptide of at least 350 amino acids comprising from the amino terminus to the carboxy terminus, a DnaJ domain, a G/F rich domain, a Cys-rich zinc finger domain, a CTD domain and a CaaX motif. Further preferably, a portion as defined above is a portion of a nucleic acid as represented by any one of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 19, SEQ ID NO: 21, SEQ ID NO: 23, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51 SEQ ID NO: 53 or SEQ ID NO: 55 of Table 1.

A portion may be prepared, for example, by making one or more deletions to a type I DnaJ-like nucleic acid. One example consists in removing polynucleotide sequences encoding specific subcellular targeting sequences, such as mitochondrial or plastidic targeting sequences. The portions may be used in isolated form or they may be fused to other coding (or non coding) sequences in order to, for example, produce a protein that combines several activities. When fused to other coding sequences, the resulting polypeptide produced upon translation could be bigger than that predicted for the type I DnaJ-like fragment. For example, an oligonucleotide coding for the farnesylation motif could be fused to a type I DnaJ-like polynucleotide sequence encoding a type I DnaJ-like polypeptide originally lacking this motif. The portion may be fused to another portion of a coding sequence of another member of the type I DnaJ family thereby replacing domains between the two original type I DnaJ-like polypeptides. For example the CTD domain of one type I DnaJ-like polypeptide may be exchanged for the CTD domain of another type I DnaJ-like polypeptide.

Another variant of a type I DnaJ-like nucleic acid/gene is a nucleic acid capable of hybridising under reduced stringency conditions, preferably under stringent conditions, with a type I DnaJ-like nucleic acid/gene as hereinbefore defined, which hybridising sequence encodes at least the J-domain and the Cys-rich zinc finger domain of a type I DnaJ-like polypeptide. Preferably such variant comprises all of the domains characterizing type I DnaJ-like polypeptides, from the amino terminus to the carboxy terminus, a DnaJ domain, a G/F rich domain, a Cys-rich zinc finger domain and a CTD domain, and additionally a CaaX motif.

Preferably, the hybridising sequence is one that is capable of hybridising to a nucleic acid as represented by any one of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 19, SEQ ID NO: 21, SEQ ID NO: 23, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51 SEQ ID NO: 53 or SEQ ID NO: 55 of Table 1 or to a portion of any of the aforementioned sequences as defined hereinabove.

The term “hybridisation” as defined herein is a process wherein substantially homologous complementary nucleotide sequences anneal to each other. The hybridisation process can occur entirely in solution, i.e. both complementary nucleic acids are in solution. The hybridisation process can also occur with one of the complementary nucleic acids immobilised to a matrix such as magnetic beads, Sepharose beads or any other resin. The hybridisation process can furthermore occur with one of the complementary nucleic acids immobilised to a solid support such as a nitrocellulose or nylon membrane or immobilised by e.g. photolithography to, for example, a siliceous glass support (the latter known as nucleic acid arrays or microarrays or as nucleic acid chips). In order to allow hybridisation to occur, the nucleic acid molecules are generally thermally or chemically denatured to melt a double strand into two single strands and/or to remove hairpins or other secondary structures from single stranded nucleic acids. The stringency of hybridisation is influenced by conditions such as temperature, salt concentration, ionic strength and hybridisation buffer composition.

“Stringent hybridisation conditions” and “stringent hybridisation wash conditions” in the context of nucleic acid hybridisation experiments such as Southern and Northern hybridisations are sequence dependent and are different under different environmental parameters. The skilled artisan is aware of various parameters which may be altered during hybridisation and washing and which will either maintain or change the stringency conditions.

The T_(m) is the temperature under defined ionic strength and pH, at which 50% of the target sequence hybridises to a perfectly matched probe. The T_(m) is dependent upon the solution conditions and the base composition and length of the probe. For example, longer sequences hybridise specifically at higher temperatures. The maximum rate of hybridisation is obtained from about 16° C. up to 32° C. below T_(m). The presence of monovalent cations in the hybridisation solution reduce the electrostatic repulsion between the two nucleic acid strands thereby promoting hybrid formation; this effect is visible for sodium concentrations of up to 0.4M. Formamide reduces the melting temperature of DNA-DNA and DNA-RNA duplexes with 0.6 to 0.7° C. for each percent formamide, and addition of 50% formamide allows hybridisation to be performed at 30 to 45° C., though the rate of hybridisation will be lowered. Base pair mismatches reduce the hybridisation rate and the thermal stability of the duplexes. On average and for large probes, the T_(m) decreases about 1° C. per % base mismatch. The T_(m) may be calculated using the following equations, depending on the types of hybrids:

-   -   1. DNA-DNA hybrids (Meinkoth and Wahl, Anal. Biochem., 138:         267-284, 1984):         -   T_(m)=81.5° C.+16.6×log             [Na⁺]^(a)+0.41×%[G/C^(b)]−500×[L^(c)]⁻¹−0.61×% formamide     -   2. DNA-RNA or RNA-RNA hybrids:         -   T_(m)=79.8+18.5 (log₁₀[Na⁺]^(a))+0.58 (% G/C^(b))+11.8 (%             G/C^(b))²−820/L^(c)     -   3. oligo-DNA or oligo-RNAd hybrids:         -   For <20 nucleotides: T_(m)=2 (I_(n))         -   For 20-35 nucleotides: T_(m)=22+1.46 (I_(n)) ^(a) or for             other monovalent cation, but only accurate in the 0.01-0.4 M             range.^(b) only accurate for % GC in the 30% to 75%             range.^(c) L=length of duplex in base pairs.^(d) Oligo,             oligonucleotide; I_(n), effective length of primer=2×(no. of             G/C)+(no. of A/T).

Note: for each 1% formamide, the T_(m) is reduced by about 0.6 to 0.7° C., while the presence of 6 M urea reduces the T_(m) by about 30° C.

Specificity of hybridisation is typically the function of post-hybridisation washes. To remove background resulting from non-specific hybridisation, samples are washed with dilute salt solutions. Critical factors of such washes include the ionic strength and temperature of the final wash solution: the lower the salt concentration and the higher the wash temperature, the higher the stringency of the wash. Wash conditions are typically performed at or below hybridisation stringency. Generally, suitable stringent conditions for nucleic acid hybridisation assays or gene amplification detection procedures are as set forth above. Conditions of greater or less stringency may also be selected. Generally, low stringency conditions are selected to be about 50° C. lower than the thermal melting point (T_(m)) for the specific sequence at a defined ionic strength and pH. Medium stringency conditions are when the temperature is 20° C. below T_(m), and high stringency conditions are when the temperature is 10° C. below T_(m). For example, stringent conditions are those that are at least as stringent as, for example, conditions A-L; and reduced stringency conditions are at least as stringent as, for example, conditions M-R. Non-specific binding may be controlled using any one of a number of known techniques such as, for example, blocking the membrane with protein containing solutions, additions of heterologous RNA, DNA, and SDS to the hybridisation buffer, and treatment with RNase. Examples of hybridisation and wash conditions are listed in Table 2 below.

TABLE 2 Examples of hybridisation and wash conditions Wash Stringency Polynucleotide Hybrid Length Hybridization Temperature Temperature Condition Hybrid^(±) (bp)^(‡) and Buffer^(†) and Buffer^(†) A DNA:DNA > or 65° C. 1 × SSC; or 42° C., 1 × SSC 65° C.; 0.3 × SSC equal to 50 and 50% formamide B DNA:DNA <50 Tb*; 1 × SSC Tb*; 1 × SSC C DNA:RNA > or 67° C. 1 × SSC; or 45° C., 1 × SSC 67° C.; 0.3 × SSC equal to 50 and 50% formamide D DNA:RNA <50 Td*; 1 × SSC Td*; 1 × SSC E RNA:RNA > or 70° C. 1 × SSC; or 50° C., 1 × SSC 70° C.; 0.3 × SSC equal to 50 and 50% formamide F RNA:RNA <50 Tf*; 1 × SSC Tf*; 1 × SSC G DNA:DNA > or 65° C. 4 × SSC; or 45° C., 4 × SSC 65° C.; 1 × SSC equal to 50 and 50% formamide H DNA:DNA <50 Th*; 4 × SSC Th*; 4 × SSC I DNA:RNA > or 67° C. 4 × SSC; or 45° C., 4 × SSC 67° C.; 1 × SSC equal to 50 and 50% formamide J DNA:RNA <50 Tj*; 4 × SSC Tj*; 4 × SSC K RNA:RNA > or 70° C. 4 × SSC; or 40° C., 6 × SSC 67° C.; 1 × SSC equal to 50 and 50% formamide L RNA:RNA <50 Tl*; 2 × SSC Tl*; 2 × SSC M DNA:DNA > or 50° C. 4 × SSC; or 40° C., 6 × SSC 50° C.; 2 × SSC equal to 50 and 50% formamide N DNA:DNA <50 Tn*; 6 × SSC Tn*; 6 × SSC O DNA:RNA > or 55° C. 4 × SSC; or 42° C., 6 × SSC 55° C.; 2 × SSC equal to 50 and 50% formamide P DNA:RNA <50 Tp*; 6 × SSC Tp*; 6 × SSC Q RNA:RNA > or 60° C. 4 × SSC; or 45° C., 6 × SSC 60° C.; 2 × SSC equal to 50 and 50% formamide R RNA:RNA <50 Tr*; 4 × SSC Tr*; 4 × SSC ^(‡)The “hybrid length” is the anticipated length for the hybridising nucleic acid. When nucleic acids of known sequence are hybridised, the hybrid length may be determined by aligning the sequences and identifying the conserved regions described herein. ^(†)SSPE (1 × SSPE is 0.15M NaCl, 10 mM NaH₂PO₄, and 1.25 mM EDTA, pH 7.4) may be substituted for SSC (1 × SSC is 0.15M NaCl and 15 mM sodium citrate) in the hybridisation and wash buffers; washes are performed for 15 minutes after hybridisation is complete. The hybridisations and washes may additionally include 5× Denhardt’s reagent, 0.5-1.0% SDS, 100 μg/ml denatured, fragmented salmon sperm DNA, 0.5% sodium pyrophosphate, and up to 50% formamide. *Tb-Tr: The hybridisation temperature for hybrids anticipated to be less than 50 base pairs in length should be 5-10° C. less than the melting temperature T_(m) of the hybrids; the T_(m) is determined according to the above-mentioned equations. ^(±)The present invention also encompasses the substitution of any one, or more DNA or RNA hybrid partners with either a PNA, or a modified nucleic acid.

For the purposes of defining the level of stringency, reference can be made to Sambrook et al., (2001) Molecular Cloning: a laboratory manual, 3^(rd) Edition Cold Spring Harbor Laboratory Press, CSH, New York or to Current Protocols in Molecular Biology, John Wiley & Sons, N.Y. (1989).

A type I DnaJ-like nucleic acid or variant thereof may be derived from any natural or artificial source. This nucleic acid may be modified from its native form in composition and/or genomic environment through deliberate human manipulation. The nucleic acid is either of prokaryotic or eukaryotic origin, from a microbial source, such as yeast or fungi, or from a plant, algae or animal (including human) source. Preferably the nucleic acid is of eukaryotic origin. The nucleic acid is further preferably of plant origin, whether from the same plant species (for example to the one in which it is to be introduced) or whether from a different plant species. The nucleic acid may be isolated from a monocotyledonous species, preferably from the family Poaceae, further preferably from Oryza sativa. More preferably, the type I DnaJ-like nucleic acid isolated from Oryza sativa is represented by SEQ ID NO: 1 and the type I DnaJ-like amino acid sequence is as represented by SEQ ID NO: 2.

The activity of a type I DnaJ-like polypeptide or a homologue thereof may be increased by introducing a genetic modification (preferably in the locus of a type I DnaJ-like gene). The locus of a gene as defined herein is taken to mean a genomic region, which includes the gene of interest and 10 KB up- or downstream of the coding region.

The genetic modification may be introduced, for example, by any one (or more) of the following methods: T-DNA activation, TILLING, site-directed mutagenesis, directed evolution and homologous recombination or by introducing and/or expressing in the cytosol of a plant cell a nucleic acid encoding a type DnaJ-like polypeptide or a homologue thereof, which type I DnaJ-like polypeptide comprises a CaaX motif at its carboxy terminus. Following introduction of the genetic modification, there follows an optional step of selecting for increased activity in the cytosol of a plant cell of a type I DnaJ-like polypeptide, which increase in activity in the gives plants having increased plant yield under non-stress conditions.

T-DNA activation tagging (Hayashi et al. Science (1992) 1350-1353) involves insertion of T-DNA usually containing a promoter (may also be a translation enhancer or an intron), in the genomic region of the gene of interest or 10 KB up- or downstream of the coding region of a gene in a configuration such that the promoter directs expression of the targeted gene. Typically, regulation of expression of the targeted gene by its natural promoter is disrupted and the gene falls under the control of the newly introduced promoter. The promoter is typically embedded in a T-DNA. This T-DNA is randomly inserted into the plant genome, for example, through Agrobacterium infection and leads to overexpression of genes near the inserted T-DNA. The resulting transgenic plants show dominant phenotypes due to overexpression of genes close to the introduced promoter. The promoter to be introduced may be any promoter capable of directing expression of a gene in the desired organism, in this case a plant. For example, constitutive, tissue-specific, cell type-specific and inducible promoters are all suitable for use in T-DNA activation. Preferably, the promoter is one capable driving expression of the gene in plant seed tissue.

A genetic modification may also be introduced in the locus of a type I DnaJ-like gene using the technique of TILLING (Targeted Induced Local Lesions In Genomes). This is a mutagenesis technology useful to generate and/or identify, and to eventually isolate mutagenised variants of a type I DnaJ-like nucleic acid capable of exhibiting DnaJ-like activity. TILLING also allows selection of plants carrying such mutant variants. These mutant variants may even exhibit higher DnaJ-like activity than that exhibited by the gene in its natural form. TILLING combines high-density mutagenesis with high-throughput screening methods. The steps typically followed in TILLING are: (a) EMS mutagenesis (Redei G P and Koncz C (1992) In Methods in Arabidopsis Research, Koncz C, Chua N H, Schell J, eds. Singapore, World Scientific Publishing Co, pp. 16-82; Feldmann et al. (1994) In Meyerowitz E M, Somerville C R, eds, Arabidopsis. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., pp 137-172; Lightner J and Caspar T (1998) In J Martinez-Zapater, J Salinas, eds, Methods on Molecular Biology, Vol. 82. Humana Press, Totowa, N.J., pp 91-104); (b) DNA preparation and pooling of individuals; (c) PCR amplification of a region of interest; (d) denaturation and annealing to allow formation of heteroduplexes; (e) DHPLC, where the presence of a heteroduplex in a pool is detected as an extra peak in the chromatogram; (f) identification of the mutant individual; and (g) sequencing of the mutant PCR product. Methods for TILLING are well known in the art (McCallum et al., (2000) Nat Biotechnol 18: 455-457; reviewed by Stemple (2004) Nat Rev Genet 5(2): 145-50).

Site-directed mutagenesis may be used to generate variants of type I DnaJ-like nucleic acids or portions thereof. Several methods are available to achieve site-directed mutagenesis, the most common being PCR based methods (Current Protocols in Molecular Biology. Wiley Eds.

Directed evolution may be used which consists of iterations of DNA shuffling followed by appropriate screening and/or selection to generate variants of type I DnaJ-like nucleic acids or portions thereof encoding type I DnaJ-like polypeptides or homologues or portions thereof having an increased biological activity (Castle et al., (2004) Science 304(5674): 1151-4; U.S. Pat. Nos. 5,811,238 and 6,395,547).

T-DNA activation, TILLING, site-directed mutagenesis and directed evolution are examples of technologies that enable the generation of novel alleles and type I DnaJ-like variants.

Homologous recombination allows introduction in a genome of a selected nucleic acid at a defined selected position. Homologous recombination is a standard technology used routinely in biological sciences for lower organisms such as yeast or the moss Physcomitrella. Methods for performing homologous recombination in plants have been described not only for model plants (Offring a et al., (1990) EMBO J 9(10): 3077-84) but also for crop plants, for example rice (Terada et al., (2002) Nat Biotech 20(10): 1030-4; lida and Terada (2004) Curr Opin Biotech 15(2):132-8). The nucleic acid to be targeted (which may be a type I DnaJ-like nucleic acid or variant thereof as hereinbefore defined) is targeted to the locus of a type I DnaJ-like gene. The nucleic acid to be targeted may be an improved allele used to replace the endogenous gene or may be introduced in addition to the endogenous gene.

According to a preferred embodiment of the invention, plant yield may be increased by introducing and/or expressing in the cytosol of a plant cell a nucleic acid encoding a type I DnaJ-like polypeptide or a homologue thereof, which type I DnaJ-like polypeptide or homologue thereof comprises a CaaX motif at its carboxy terminus.

A preferred method for introducing a genetic modification (which in this case need not be in the locus of a type I DnaJ-like gene) is to introduce and/or express in the cytosol of a plant cell an exogenous nucleic acid encoding a type I DnaJ-like polypeptide or a homologue thereof, which exogenous type I DnaJ-like polypeptide or a homologue thereof comprises a CaaX motif at its carboxy terminus. The nucleic acid to be introduced into a plant may be a full-length nucleic acid or may be a portion or a hybridizing sequence as hereinbefore defined.

The term “exogenous” as defined herein refers to an isolated gene/nucleic acid, which may be from the same or different plant species, for example an isolated rice gene/nucleic acid introduced and/or expressed in a rice plant is “exogenous” according to the definition above.

“Homologues” of a protein encompass peptides, oligopeptides, polypeptides, proteins and enzymes having amino acid substitutions, deletions and/or insertions relative to the unmodified protein in question and having similar biological and functional activity as the unmodified protein from which they are derived. To produce such homologues, amino acids of the protein may be replaced by other amino acids having similar properties (such as similar hydrophobicity, hydrophilicity, antigenicity, propensity to form or break α-helical structures or β-sheet structures). Conservative substitution tables are well known in the art (see for example Creighton (1984) Proteins. W.H. Freeman and Company). Table 3 below gives examples of conserved amino acid substitutions.

TABLE 2 Examples of conserved amino acid substitutions Residue Conservative Substitutions Ala Ser Arg Lys Asn Gln; His Asp Glu Gln Asn Cys Ser Glu Asp Gly Pro His Asn; Gln Ile Leu, Val Leu Ile; Val Lys Arg; Gln Met Leu; Ile Phe Met; Leu; Tyr Ser Thr; Gly Thr Ser; Val Trp Tyr Tyr Trp; Phe Val Ile; Leu

Homologues include orthologues and paralogoues, which encompass evolutionary concepts used to describe ancestral relationships of genes. Paralogues are genes within the same species that have originated through duplication of an ancestral gene and orthologues are genes from different organisms that have originated through speciation.

Orthologues in, for example, monocot plant species may easily be found by performing a so-called reciprocal blast search. This may be done by a first blast involving blasting a query sequence (for example, SEQ ID NO: 1 or SEQ ID NO: 2) against any sequence database, such as the publicly available NCBI database which may be found at the NCBI web site. BLASTN or TBLASTX (using standard default values) may be used when starting from a nucleotide sequence and BLASTP or TBLASTN (using standard default values) may be used when starting from a protein sequence. The BLAST results may optionally be filtered. The full-length sequences of either the filtered results or non-filtered results are then BLASTed back (second BLAST) against sequences from the organism from which the query sequence is derived (where the query sequence is SEQ ID NO: 1 or SEQ ID NO: 2 the second blast would therefore be against rice sequences). The results of the first and second BLASTs are then compared. A paralogue is identified if a high-ranking hit from the second blast is from the same species as from which the query sequence is derived; an orthologue is identified if a high-ranking hit is not from the same species as from which the query sequence is derived. High-ranking hits are those having a low E-value. The lower the E-value, the more significant the score (or in other words the lower the chance that the hit was found by chance). Computation of the E-value is well known in the art. In the case of large families, ClustalW may be used, followed by a neighbour joining tree, to help visualize clustering of related genes and to identify orthologues and paralogues.

A homologue may be in the form of a “substitutional variant” of a protein, i.e. where at least one residue in an amino acid sequence has been removed and a different residue inserted in its place. Amino acid substitutions are typically of single residues, but may be clustered depending upon functional constraints placed upon the polypeptide; insertions will usually be of the order of about 1 to 10 amino acid residues. Preferably, amino acid substitutions comprise conservative amino acid substitutions (see Table 3 above).

A homologue may also be in the form of an “insertional variant” of a protein, i.e. where one or more amino acid residues are introduced into a predetermined site in a protein. Insertions may comprise amino-terminal and/or carboxy-terminal fusions as well as intra-sequence insertions of single or multiple amino acids. Generally, insertions within the amino acid sequence will be smaller than amino- or carboxy-terminal fusions, of the order of about 1 to 10 residues. Examples of amino- or carboxy-terminal fusion proteins or peptides include the binding domain or activation domain of a transcriptional activator as used in the yeast two-hybrid system, phage coat proteins, (histidine)6-tag, glutathione S-transferase-tag, protein A, maltose-binding protein, dihydrofolate reductase, Tag-100 epitope, c-myc epitope, FLAG-epitope, lacZ, CMP (calmodulin-binding peptide), HA epitope, protein C epitope and VSV epitope.

Homologues in the form of “deletion variants” of a protein are characterised by the removal of one or more amino acids from a protein. One example of such a deletion variant is to remove the mitochondrial or plastidic targeting sequences from type I DnaJ-like proteins otherwise targeted to these organelles.

Amino acid variants of a protein may readily be made using peptide synthetic techniques well known in the art, such as solid phase peptide synthesis and the like, or by recombinant DNA manipulation. Methods for the manipulation of DNA sequences to produce substitution, insertion or deletion variants of a protein are well known in the art. For example, techniques for making substitution mutations at predetermined sites in DNA are well known to those skilled in the art and include M13 mutagenesis, T7-Gen in vitro mutagenesis (USB, Cleveland, Ohio), QuickChange Site Directed mutagenesis (Stratagene, San Diego, Calif.), PCR-mediated site-directed mutagenesis or other site-directed mutagenesis protocols.

The type I DnaJ-like polypeptide or homologue thereof may be a derivative. “Derivatives” include peptides, oligopeptides, polypeptides, proteins and enzymes which may comprise substitutions, deletions or additions of naturally and non-naturally occurring amino acid residues compared to the amino acid sequence of a naturally-occurring form of the protein, for example, as presented in SEQ ID NO: 2. “Derivatives” of a protein encompass peptides, oligopeptides, polypeptides, proteins and enzymes which may comprise naturally occurring altered, glycosylated, acylated, prenylated or non-naturally occurring amino acid residues compared to the amino acid sequence of a naturally-occurring form of the polypeptide. A derivative may also comprise one or more non-amino acid substituents compared to the amino acid sequence from which it is derived, for example a reporter molecule or other ligand, covalently or non-covalently bound to the amino acid sequence, such as a reporter molecule which is bound to facilitate its detection, and non-naturally occurring amino acid residues relative to the amino acid sequence of a naturally-occurring protein.

The type I DnaJ-like polypeptide or homologue thereof may be encoded by an alternative splice variant of a type I DnaJ-like nucleic acid/gene. The term “alternative splice variant” as used herein encompasses variants of a nucleic acid sequence in which selected introns and/or exons have been excised, replaced or added, or in which introns have been shortened or lengthened. Such variants will be ones in which the biological activity of the protein is retained, which may be achieved by selectively retaining functional segments of the protein. Such splice variants may be found in nature or may be manmade. Methods for making such splice variants are well known in the art. Preferred are splice variants encoding a polypeptide being a type I DnaJ-like polypeptide or a homologue thereof, which type I DnaJ-like polypeptide or homologue thereof comprises a CaaX motif at its carboxy terminus, particularly splice variants of SEQ ID NO: 1.

The homologue may also be encoded by an allelic variant of a nucleic acid encoding a type I DnaJ-like polypeptide or a homologue thereof, preferably an allelic variant of the nucleic acid represented by SEQ ID NO: 1. Further preferably, the polypeptide encoded by the allelic variant is a type I DnaJ-like polypeptide or a homologue thereof, which type I DnaJ-like polypeptide or homologue thereof comprises a CaaX motif at its carboxy terminus.

Allelic variants exist in nature, and encompassed within the methods of the present invention is the use of these natural alleles. Allelic variants encompass Single Nucleotide Polymorphisms (SNPs), as well as Small Insertion/Deletion Polymorphisms (INDELs). The size of INDELs is usually less than 100 bp. SNPs and INDELs form the largest set of sequence variants in naturally occurring polymorphic strains of most organisms.

According to a preferred aspect of the present invention, enhanced or increased expression of the type I DnaJ-like nucleic acid or variant thereof is envisaged. Methods for obtaining enhanced or increased expression of genes or gene products are well documented in the art and include, for example, overexpression driven by appropriate promoters, the use of transcription enhancers or translation enhancers. Isolated nucleic acids which serve as promoter or enhancer elements may be introduced in an appropriate position (typically upstream) of a non-heterologous form of a polynucleotide so as to upregulate expression of a type I DnaJ-like nucleic acid or variant thereof. For example, endogenous promoters may be altered in vivo by mutation, deletion, and/or substitution (see, Kmiec, U.S. Pat. No. 5,565,350; Zarling et al., PCT/US93/03868), or isolated promoters may be introduced into a plant cell in the proper orientation and distance from a gene of the present invention so as to control the expression of the gene.

If polypeptide expression is desired, it is generally desirable to include a polyadenylation region at the 3′-end of a polynucleotide coding region. The polyadenylation region can be derived from the natural gene, from a variety of other plant genes, or from T-DNA. The 3′ end sequence to be added may be derived from, for example, the nopaline synthase or octopine synthase genes, or alternatively from another plant gene, or less preferably from any other eukaryotic gene.

An intron sequence may also be added to the 5′ untranslated region or the coding sequence of the partial coding sequence to increase the amount of the mature message that accumulates in the cytosol. Inclusion of a spliceable intron in the transcription unit in both plant and animal expression constructs has been shown to increase gene expression at both the mRNA and protein levels up to 1000-fold, Buchman and Berg, Mol. Cell biol. 8:4395-4405 (1988); Callis et al., Genes Dev. 1:1183-1200 (1987). Such intron enhancement of gene expression is typically greatest when placed near the 5′ end of the transcription unit. Use of the maize introns Adh1-S intron 1, 2, and 6, the Bronze-1 intron are known in the art. See generally, The Maize Handbook, Chapter 116, Freeling and Walbot, Eds., Springer, N.Y. (1994).

The invention also provides genetic constructs and vectors to facilitate introduction and/or expression of the nucleotide sequences useful in the methods according to the invention.

Therefore, there is provided a gene construct comprising:

-   -   (i) a nucleic acid or variant thereof encoding a type I         DnaJ-like polypeptide or a homologue thereof, which type I         DnaJ-like polypeptide or homologue thereof comprises a CaaX         motif at its carboxy terminus; and     -   (ii) one or more control sequences capable of driving expression         of the nucleic acid sequence of (i); and optionally     -   (iii) a transcription termination sequence.

Also provided by the present invention is the use of a construct, as defined herein, in methods for increasing plant yield in plants grown under non-stress conditions.

Constructs useful in the methods according to the present invention may be constructed using recombinant DNA technology well known to persons skilled in the art. The gene constructs may be inserted into vectors, which may be commercially available, suitable for transforming into plants and suitable for expression of the gene of interest in the transformed cells.

Plants are transformed with a vector comprising the sequence of interest (i.e., nucleic acid or variant thereof encoding a type I DnaJ-like polypeptide or homologue thereof that comprises a CaaX motif at its carboxy terminus). The sequence of interest is operably linked to one or more control sequences (at least to a promoter). The terms “regulatory element”, “control sequence” and “promoter” are all used interchangeably herein and are to be taken in a broad context to refer to regulatory nucleic acid sequences capable of effecting expression of the sequences to which they are ligated. Encompassed by the aforementioned terms are transcriptional regulatory sequences derived from a classical eukaryotic genomic gene (including the TATA box which is required for accurate transcription initiation, with or without a CCAAT box sequence) and additional regulatory elements (i.e. upstream activating sequences, enhancers and silencers) which alter gene expression in response to developmental and/or external stimuli, or in a tissue-specific manner. Also included within the term is a transcriptional regulatory sequence of a classical prokaryotic gene, in which case it may include a −35 box sequence and/or −10 box transcriptional regulatory sequences. The term “regulatory element” also encompasses a synthetic fusion molecule or derivative that confers, activates or enhances expression of a nucleic acid molecule in a cell, tissue or organ. The term “operably linked” as used herein refers to a functional linkage between the promoter sequence and the gene of interest, such that the promoter sequence is able to initiate transcription of the gene of interest.

Advantageously, any type of promoter, whether natural or synthetic, may be used to drive expression of the nucleic acid sequence. Preferably, the promoter is a tissue-specific promoter, i.e. one that is capable of preferentially initiating transcription in certain tissues, such as the leaves, roots, seed tissue etc. Plant-derived promoters are particularly preferred, especially plant-derived tissue-specific promoters. The term “tissue-specific” as defined herein refers to a promoter that is expressed predominantly in at least one plant tissue or organ, but which may have residual expression elsewhere in the plant due to leaky promoter expression. Further preferably, the tissue-specific promoter is a seed-specific promoter, more particularly a promoter isolated from a gene encoding a seed-storage protein, especially an endosperm-specific promoter. Most preferably the endosperm-specific promoter is isolated from a prolamin gene, such as a rice prolamin RP6 (Wen et al. (1993) Plant Physiol 101(3): 1115-6) promoter as represented by SEQ ID NO: 57, or a promoter of similar strength and/or a promoter with a similar expression pattern as the rice prolamin promoter. Similar strength and/or similar expression pattern may be analysed, for example, by coupling the promoters to a reporter gene and checking the function of the reporter gene in tissues of the plant. One well-known reporter gene is beta-glucuronidase and the calorimetric GUS stain used to visualize beta-glucuronidase activity in plant tissue. It should be clear that the applicability of the present invention is not restricted to the type I DnaJ-like nucleic acid represented by SEQ ID NO: 1, nor is the applicability of the invention restricted to expression of a type I DnaJ-like nucleic acid when driven by a prolamin promoter.

Examples of seed-specific promoters are presented in Table 4, which promoters or derivatives thereof are useful in performing the methods of the present invention. It should be understood that the list below is not exhaustive.

TABLE 4 Examples of seed-specific promoters for use in the present invention EXPRESSION GENE SOURCE PATTERN REFERENCE seed-specific genes seed Simon, et al., Plant Mol. Biol. 5: 191, 1985; Scofield, et al., J. Biol. Chem. 262: 12202, 1987; Baszczynski, et al., Plant Mol. Biol. 14: 633, 1990. Brazil Nut albumin seed Pearson, et al., Plant Mol. Biol. 18: 235-245, 1992. legumin seed Ellis, et al., Plant Mol. Biol. 10: 203- 214, 1988. glutelin (rice) seed Takaiwa, et al., Mol. Gen. Genet. 208: 15-22, 1986; Takaiwa, et al., FEBS Letts. 221: 43-47, 1987. zein seed Matzke et al Plant Mol Biol, 14(3): 323-32 1990. napA seed Stalberg, et al., Planta 199: 515-519, 1996. wheat LMW and HMW endosperm Mol Gen Genet 216: 81-90, 1989; glutenin-1 NAR 17: 461-2, 1989. wheat SPA seed Albani et al., Plant Cell, 9: 171-184, 1997. wheat α, β, γ-gliadins endosperm EMBO 3: 1409-15, 1984. barley ltr1 promoter endosperm barley B1, C, D, endosperm Theor Appl Gen 98: 1253-62, 1999; hordein Plant J 4: 343-55, 1993; Mol Gen Genet 250: 750-60, 1996. barley DOF endosperm Mena et al., The Plant Journal, 116(1): 53-62, 1998. blz2 endosperm EP99106056.7 synthetic promoter endosperm Vicente-Carbajosa et al., Plant J. 13: 629-640, 1998. rice prolamin NRP33 endosperm Wu et al., Plant Cell Physiology 39(8) 885-889, 1998. rice α-globulin Glb-1 endosperm Wu et al., Plant Cell Physiology 39(8) 885-889, 1998. rice OSH1 embryo Sato et al., Proc. Natl. Acad. Sci. USA, 93: 8117-8122, 1996. rice α-globulin endosperm Nakase et al., Plant Mol. Biol. 33: 513- REB/OHP-1 522, 1997. rice ADP-glucose PP endosperm Trans Res 6: 157-68, 1997. maize ESR gene family endosperm Plant J 12: 235-46, 1997. sorgum γ-kafirin endosperm PMB 32: 1029-35, 1996. KNOX embryo Postma-Haarsma et al., Plant Mol. Biol. 39: 257-71, 1999. rice oleosin embryo and aleurone Wu et al., J. Biochem., 123: 386, 1998. sunflower oleosin seed (embryo and Cummins, et al., Plant Mol. Biol. 19: dry seed) 873-876, 1992.

Optionally, one or more terminator sequences may also be used in the construct introduced into a plant. The term “terminator” encompasses a control sequence which is a DNA sequence at the end of a transcriptional unit which signals 3′ processing and polyadenylation of a primary transcript and termination of transcription. Additional regulatory elements may include transcriptional as well as translational enhancers. Those skilled in the art will be aware of terminator and enhancer sequences that may be suitable for use in performing the invention. Such sequences would be known or may readily be obtained by a person skilled in the art.

The genetic constructs of the invention may further include an origin of replication sequence that is required for maintenance and/or replication in a specific cell type. One example is when a genetic construct is required to be maintained in a bacterial cell as an episomal genetic element (e.g. plasmid or cosmid molecule). Preferred origins of replication include, but are not limited to, the f1-ori and colE1.

The genetic construct may optionally comprise a selectable marker gene. As used herein, the term “selectable marker gene” includes any gene that confers a phenotype on a cell in which it is expressed to facilitate the identification and/or selection of cells that are transfected or transformed with a nucleic acid construct of the invention. Suitable markers may be selected from markers that confer antibiotic or herbicide resistance, that introduce a new metabolic trait or that allow visual selection. Examples of selectable marker genes include genes conferring resistance to antibiotics (such as nptII that phosphorylates neomycin and kanamycin, or hptII, phosphorylating hygromycin), to herbicides (for example bar which provides resistance to Basta; aroA or gox providing resistance against glyphosate), or genes that provide a metabolic trait (such as manA that allows plants to use mannose as sole carbon source). Visual marker genes result in the formation of colour (for example β-glucuronidase, GUS), luminescence (such as luciferase) or fluorescence (Green Fluorescent Protein, GFP, and derivatives thereof).

The present invention also encompasses plants and plant parts obtainable by the methods according to the present invention. The present invention therefore provides plants and parts thereof obtainable by the methods according to the present invention, which plants have introduced therein a nucleic acid or variant thereof encoding a type I DnaJ-like polypeptide or a homologue thereof, which type I DnaJ-like polypeptide or homologue thereof comprises a CaaX motif at its carboxy terminus.

The invention also provides a method for the production of transgenic plants having increased plant yield when grown under non-stress conditions, comprising introduction and/or expression in the cytosol of a plant cell of a nucleic acid or a variant thereof encoding a type I DnaJ-like polypeptide or a homologue thereof, which type I DnaJ-like polypeptide or homologue thereof comprises a CaaX motif at its carboxy terminus.

More specifically, the present invention provides a method for the production of transgenic plants with increased yield which method comprises:

-   -   (i) introducing and/or expressing in the cytosol of plant,         plants part or plant cell a nucleic acid or variant thereof         encoding a type I DnaJ-like polypeptide or a homologue thereof,         which type I DnaJ-like polypeptide or homologue thereof         comprises a CaaX motif at its carboxy terminus; and     -   (ii) cultivating the plant, plant part or plant cell under         non-stress conditions promoting plant growth and development.

The nucleic acid may be introduced directly into a plant cell or into the plant itself (including introduction into a tissue, organ or any other part of a plant). According to a preferred feature of the present invention, the nucleic acid is preferably introduced into a plant by transformation.

The term “transformation” as referred to herein encompasses the transfer of an exogenous polynucleotide into a host cell, irrespective of the method used for transfer. Plant tissue capable of subsequent clonal propagation, whether by organogenesis or embryogenesis, may be transformed with a genetic construct of the present invention and a whole plant regenerated there from. The particular tissue chosen will vary depending on the clonal propagation systems available for, and best suited to, the particular species being transformed. Exemplary tissue targets include leaf disks, pollen, embryos, cotyledons, hypocotyls, megagametophytes, callus tissue, existing meristematic tissue (e.g., apical meristem, axillary buds, and root meristems), and induced meristem tissue (e.g., cotyledon meristem and hypocotyl meristem). The polynucleotide may be transiently or stably introduced into a host cell and may be maintained non-integrated, for example, as a plasmid. Alternatively, it may be integrated into the host genome. The resulting transformed plant cell may then be used to regenerate a transformed plant in a manner known to persons skilled in the art.

Transformation of plant species is now a fairly routine technique. Advantageously, any of several transformation methods may be used to introduce the gene of interest into a suitable ancestor cell. Transformation methods include the use of liposomes, electroporation, chemicals that increase free DNA uptake, injection of the DNA directly into the plant, particle gun bombardment, transformation using viruses or pollen and microprojection. Methods may be selected from the calcium/polyethylene glycol method for protoplasts (Krens F A et al., (1982) Nature 296, 72-74; Negrutiu I et al. (1987) Plant Mol Biol 8: 363-373); electroporation of protoplasts (Shillito R D et al. 1985 Bio/Technol 3, 1099-1102); microinjection into plant material (Crossway A et al. (1986) Mol. Gen Genet 202: 179-185); DNA or RNA-coated particle bombardment (Klein T M et al. (1987) Nature 327: 70) infection with (non-integrative) viruses and the like. Transgenic rice plants expressing a type I DnaJ-like nucleic acid/gene are preferably produced via Agrobacterium-mediated transformation using any of the well known methods for rice transformation, such as described in any of the following: published European patent application EP 1198985 A1, Aldemita and Hodges (Planta 199: 612-617, 1996); Chan et al. (Plant Mol Biol 22 (3): 491-506, 1993), Hiei et al. (Plant J 6 (2): 271-282, 1994), which disclosures are incorporated by reference herein as if fully set forth. In the case of corn transformation, the preferred method is as described in either Ishida et al, (Nat. Biotechnol 14(6): 745-50, 1996) or Frame et al, (Plant Physiol 129(1): 13-22, 2002), which disclosures are incorporated by reference herein as if fully set forth.

Generally after transformation, plant cells or cell groupings are selected for the presence of one or more markers which are encoded by plant-expressible genes co-transferred with the gene of interest, following which the transformed material is regenerated into a whole plant.

Following DNA transfer and regeneration, putatively transformed plants may be evaluated, for instance using Southern analysis, for the presence of the gene of interest, copy number and/or genomic organisation. Alternatively or additionally, expression levels of the newly introduced DNA may be monitored using Northern and/or Western analysis, both techniques being well known to persons having ordinary skill in the art.

The generated transformed plants may be propagated by a variety of means, such as by clonal propagation or classical breeding techniques. For example, a first generation (or T1) transformed plant may be selfed to give homozygous second generation (or T2) transformants, and the T2 plants further propagated through classical breeding techniques.

The generated transformed organisms may take a variety of forms. For example, they may be chimeras of transformed cells and non-transformed cells; clonal transformants (e.g., all cells transformed to contain the expression cassette); grafts of transformed and untransformed tissues (e.g., in plants, a transformed rootstock grafted to an untransformed scion).

The present invention clearly extends to any plant cell or plant produced by any of the methods described herein, and to all plant parts and propagules thereof. The present invention extends further to encompass the progeny of a primary transformed or transfected cell, tissue, organ or whole plant that has been produced by any of the aforementioned methods, the only requirement being that progeny exhibit the same genotypic and/or phenotypic characteristic(s) as those produced in the parent by the methods according to the invention. The invention also includes host cells containing an isolated type I DnaJ-like nucleic acid or variant thereof. Preferred host cells according to the invention are plant cells. The invention also extends to harvestable parts of a plant such as but not limited to seeds, leaves, fruits, flowers, stem cultures, rhizomes, tubers and bulbs. The invention furthermore relates to products derived, preferably directly derived from a harvestable part of such a plant, such products may be dry pellets or powders, oils, fats and fatty acids, starch or proteins.

The present invention also encompasses the use of type I DnaJ-like nucleic acids or variants thereof and the use of type I DnaJ-like polypeptides or homologues thereof, which type I DnaJ-like polypeptide or homologue thereof comprises a CaaX motif at its carboxy terminus. One such use relates to improving plant yield, especially in increasing yield as defined hereinabove.

Type I DnaJ-like nucleic acids or variants thereof, or type I DnaJ-like polypeptides or homologues thereof, may find use in breeding programmes in which a DNA marker is identified which may be genetically linked to a type I DnaJ-like gene or variant thereof. The type I DnaJ-like nucleic acids/genes or variants thereof, or type I DnaJ-like polypeptides or homologues thereof may be used to define a molecular marker. This DNA or protein marker may then be used in breeding programmes to select plants having increased plant yield. The type I DnaJ-like gene or variant thereof may, for example, be a nucleic acid as represented by any one of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 19, SEQ ID NO: 21, SEQ ID NO: 23, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51 SEQ ID NO: 53 or SEQ ID NO: 55 of Table 1.

Allelic variants of a type I DnaJ-like nucleic acid/gene may also find use in marker-assisted breeding programmes. Such breeding programmes sometimes require introduction of allelic variation by mutagenic treatment of the plants, using for example EMS mutagenesis; alternatively, the programme may start with a collection of allelic variants of so called “natural” origin caused unintentionally. Identification of allelic variants then takes place, for example, by PCR. This is followed by a step for selection of superior allelic variants of the sequence in question and which give increased yield in a plant. Selection is typically carried out by monitoring yield performance of plants containing different allelic variants of the sequence in question, for example, different allelic variants of any one of SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO: 19, SEQ ID NO: 21, SEQ ID NO: 23, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, SEQ ID NO: 33, SEQ ID NO: 35, SEQ ID NO: 37, SEQ ID NO: 39, SEQ ID NO: 41, SEQ ID NO: 43, SEQ ID NO: 45, SEQ ID NO: 47, SEQ ID NO: 49, SEQ ID NO: 51 SEQ ID NO: 53 or SEQ ID NO: 55 of Table 1. Yield performance may be monitored in a greenhouse or in the field. Further optional steps include crossing plants, in which the superior allelic variant was identified, with another plant. This could be used, for example, to make a combination of interesting phenotypic features. A type I DnaJ-like nucleic acid or variant thereof may also be used as probes for genetically and physically mapping the genes that they are a part of, and as markers for traits linked to those genes. Such information may be useful in plant breeding in order to develop lines with desired phenotypes. Such use of type I DnaJ-like nucleic acids or variants thereof requires only a nucleic acid sequence of at least 15 nucleotides in length. The type I DnaJ-like nucleic acids or variants thereof may be used as restriction fragment length polymorphism (RFLP) markers. Southern blots (Sambrook J, Fritsch E F and Maniatis T (1989) Molecular Cloning, A Laboratory Manual) of restriction-digested plant genomic DNA may be probed with the type I DnaJ-like nucleic acids or variants thereof. The resulting banding patterns may then be subjected to genetic analyses using computer programs such as MapMaker (Lander et al., (1987) Genomics 1: 174-181) in order to construct a genetic map. In addition, the nucleic acids may be used to probe Southern blots containing restriction endonuclease-treated genomic DNAs of a set of individuals representing parent and progeny of a defined genetic cross. Segregation of the DNA polymorphisms is noted and used to calculate the position of the type I DnaJ-like nucleic acid or variant thereof in the genetic map previously obtained using this population (Botstein et al. (1980) Am. J. Hum. Genet. 32:314-331).

The production and use of plant gene-derived probes for use in genetic mapping is described in Bematzky and Tanksley (1986) Plant Mol. Biol. Reporter 4: 37-41. Numerous publications describe genetic mapping of specific cDNA clones using the methodology outlined above or variations thereof. For example, F2 intercross populations, backcross populations, randomly mated populations, near isogenic lines, and other sets of individuals may be used for mapping. Such methodologies are well known to those skilled in the art.

The nucleic acid probes may also be used for physical mapping (i.e., placement of sequences on physical maps; see Hoheisel et al. in: Non-mammalian Genomic Analysis: A Practical Guide, Academic press 1996, pp. 319-346, and references cited therein).

In another embodiment, the nucleic acid probes may be used in direct fluorescence in situ hybridization (FISH) mapping (Trask (1991) Trends Genet. 7:149-154). Although current methods of FISH mapping favour use of large clones (several kb to several hundred kb; see Laan et al. (1995) Genome Res. 5:13-20), improvements in sensitivity may allow performance of FISH mapping using shorter probes.

A variety of nucleic acid amplification-based methods for genetic and physical mapping may be carried out using the nucleic acids. Examples include allele-specific amplification (Kazazian (1989) J. Lab. Clin. Med 11:95-96), polymorphism of PCR-amplified fragments (CAPS; Sheffield et al. (1993) Genomics 16:325-332), allele-specific ligation (Landegren et al., (1988) Science 241:1077-1080), nucleotide extension reactions (Sokolov (1990) Nucleic Acid Res. 18:3671), Radiation Hybrid Mapping (Walter et al., (1997) Nat. Genet. 7:22-28) and Happy Mapping (Dear and Cook (1989) Nucleic Acid Res. 17:6795-6807). For these methods, the sequence of a nucleic acid is used to design and produce primer pairs for use in the amplification reaction or in primer extension reactions. The design of such primers is well known to those skilled in the art. In methods employing PCR-based genetic mapping, it may be necessary to identify DNA sequence differences between the parents of the mapping cross in the region corresponding to the instant nucleic acid sequence. This, however, is generally not necessary for mapping methods.

Performance of the methods according to the present invention result in plants having increased plant yield in plants grown under non-stress conditions, as described hereinbefore. This increased plant yield may also be combined with other economically advantageous traits, such as further yield-enhancing traits, tolerance to various stresses, traits modifying various architectural features and/or biochemical and/or physiological features.

DESCRIPTION OF FIGURES

The present invention will now be described with reference to the following figures in which:

FIG. 1 shows the typical domain structure of type I DnaJ-like polypeptide. The J domain is located at the amino terminal end of the protein and encodes an HSP70-binding domain comprising the highly conserved HPD tripeptide. The G/F domain rich in glycine and phenylalanine is specifying target proteins for Hsp70 chaperone activity. The four cysteine-rich domains are involved in the coordination of zinc, with two zinc ions per type I DnaJ monomer. The CTD domain is the less conserved of the four domains defined, and may comprise a farnesylation motif CaaX.

FIG. 2 shows a multiple alignment of several type I DnaJ-like proteins from the Table 1, using VNTI AlignX multiple alignment program, based on a modified ClustalW algorithm (InforMax, Bethesda, Md. ), with default settings for gap opening penalty of 10 and a gap extension of 0.05). The J domain is double-underlined, its four helices represented as grey boxes and its conserved HPD tripeptide boxed. The G/F domain is dotted-underlined. The two zinc binding domains I and II and their conserved CxxCxGxG (SEQ ID NO: 66) are boxed. In the CTD domain, the farnesylation motif is boxed. The sequences aligned are: Musmu_mDj3 (SEQ ID NO: 5), Homsa_DNAJA2 (SEQ ID NO: 54), Homsa_HsJ2 (SEQ ID NO: 50), Sacce_YDJ1 (SEQ ID NO: 52), Ceael_DNaJ (SEQ ID NO: 48), Orysa_DNAJ CASQ SEQ ID NO: 44), Triae_DNAJ II CASQ (SEQ ID NO: 46), Arath_AtJ3 CAAX (SEQ ID NO: 20), Arath_AtJ2 CAAX (SEQ ID NO: 18), Orysa_DNAJ IV CAAX (SEQ ID NO: 8), Zeama_ZMDJ1 (SEQ ID NO: 10), Orysa_DNAJ II CAAX (SEQ ID NO: 4), Hevbr_DNAJ (SEQ ID NO: 30), Lyces_DNAJ (SEQ ID NO: 32), Glyma_pm37 DNAJ (SEQ ID NO: 28), Salgi_DNAJ2 (SEQ ID NO: 38), Triae_DNAJ (SEQ ID NO: 16), Salgi_DNAJ (SEQ ID NO: 40), Atrnu_DNAJ (SEQ ID NO:22), Medsa_DNAJ (SEQ ID NO:34), Zeama_DNAJ (SEQ ID NO: 12), Cucsa_DNAJ-1 (SEQ ID NO: 24), Solto_DNAJ (SEQ ID NO: 42), Dauca_J1P (SEQ ID NO:26), Nicta_DNAJ (SEQ ID NO: 36), CDS 1877 OsDNAJ (SEQ ID NO:2), Orysa_DNAJ III CAAX (SEQ ID NO:6), and Zeama_DNAJ CAAX (SEQ ID NO: 14).

FIG. 3 shows an alignment of type I DnaJ-like polypeptides from Arabidopsis thaliana as disclosed in the table below. The J domain is double underlined, the G/F domain is underlined in bold, the two zinc binding domains I and II and their conserved CxxCxGxG (SEQ ID NO: 66) are boxed, and the CTD is single underlined. The farnesylation motif CaaX at the carboxy terminus of the proteins is represented in bold when present. The amino acid sequences preceding the J domain (separated by a parenthesis; approximate location) represent subcellular targeting sequences. The sequences are: At5g22060 AtJ2 CAAX (SEQ ID NO: 18), At3g44110 AtJ3 CAAX (SEQ ID NO: 20), At1g28210 (SEQ ID NO: 60), At1g80030 (SEQ ID NO: 61), At2g22360 (SEQ ID NO: 62), At3g17830 (SEQ ID NO: 63), At4g39960 (SEQ ID NO: 64), and At5b48030 GFA2 (SEQ ID NO: 65).

MIPS accession NCBI protein number accession number At3g44110 S71199 At5g22060 AAB86799.1 At1g28210 NP849719 At1g80030 AAK60328 At2g22360 AAD22362 At3g17830 NM112664 At4g39960 AAL36077 At5g48030 BAB11067

FIG. 4 shows a binary vector for expression in Oryza sativa of an Oryza sativa type I DnaJ-like (internal reference CDS1877) under the control of a prolamin promoter (internal reference PRO0090).

FIG. 5 details examples of polynucleotide (from start to stop) and polypeptide sequences useful in performing the methods according to the present invention.

EXAMPLES

The present invention will now be described with reference to the following examples, which are by way of illustration alone.

DNA manipulation: unless otherwise stated, recombinant DNA techniques are performed according to standard protocols described in (Sambrook (2001) Molecular Cloning: a laboratory manual, 3rd Edition Cold Spring Harbor Laboratory Press, CSH, New York) or in Volumes 1 and 2 of Ausubel et al., (1994), Current Protocols in Molecular Biology, Current Protocols. Standard materials and methods for plant molecular work are described in Plant Molecular Biology Labfase (1993) by R. D. D. Croy, published by BIOS Scientific Publications Ltd (UK) and Blackwell Scientific Publications (UK).

Example 1 Gene Cloning

The Oryza sativa type I DnaJ-like gene (CDS1877) was amplified by PCR using as template an Oryza sativa seedling cDNA library (Invitrogen, Paisley, UK). After reverse transcription of RNA extracted from seedlings, the cDNAs were cloned into pCMV Sport 6.0. Average insert size of the bank was 1.6 kb and the original number of clones was of the order of 1.67×10⁷ cfu. Original titer was determined to be 3.34×10⁶ cfu/ml after first amplification of 6×10¹⁰ cfu/ml. After plasmid extraction, 200 ng of template was used in a 50 μl PCR mix. Primers prmO4266 (SEQ ID NO: 58; sense, start codon in bold, AttB1 site in italic: 5′ GGGGACAAG TTTGTACAAAAAAGCAGGCTTCACAATGTACGGACGCATGCC 3′) and prm04267 (SEQ ID NO: 59; reverse, complementary, stop in bold, AttB2 site in italic: 5′ GGGGACCACTTTGTACAAGAAAGCTGGGTGCATCGAATTGTTCTTACTGC 3′), which include the AttB sites for Gateway recombination, were used for PCR amplification. PCR was performed using Hifi Taq DNA polymerase in standard conditions. A PCR fragment of 1340 bp (including attB sites) was amplified and purified also using standard methods. The first step of the Gateway procedure, the BP reaction, was then performed, during which the PCR fragment recombines in vivo with the pDONR201 plasmid to produce, according to the Gateway terminology, an “entry clone”, p04452. Plasmid pDONR201 was purchased from Invitrogen, as part of the Gateway® technology.

Example 2 Vector Construction

The entry clone p04452 was subsequently used in an LR reaction with p00830, a destination vector used for Oryza sativa transformation. This vector contains as functional elements within the T-DNA borders: a plant selectable marker; a screenable marker expression cassette; and a Gateway cassette intended for LR in vivo recombination with the sequence of interest already cloned in the entry clone. A rice RP6 prolamin promoter (SEQ ID NO: 57; Wen et al. (1993) Plant Physiol 101(3): 11156) for endosperm-specific expression (PRO0090) was located upstream of this Gateway cassette.

After the LR recombination step, the resulting expression vector p072 (FIG. 4) was transformed into Agrobacterium strain LBA4044 and subsequently to Oryza sativa plants. Transformed rice plants were allowed to grow and were then examined for the parameters described in Example 3.

Example 3 Evaluation and Results of Type I DnaJ-Like Under the Control of the Rice RP6 Promoter

Approximately 15 to 20 independent TO rice transformants were generated. The primary transformants were transferred from a tissue culture chamber to a greenhouse for growing and harvest of T1 seed. 5 events, of which the T1 progeny segregated 3:1 for presence/absence of the transgene, were retained. For each of these events, approximately 10 T1 seedlings containing the transgene (hetero- and homo-zygotes) and approximately 10 T1 seedlings lacking the transgene (nullizygotes) were selected by monitoring visual marker expression. 4 T1 events were further evaluated in the T2 generation following the same evaluation procedure as for the T1 generation but with more individuals per event.

Statistical Analysis: F-Test

A two factor ANOVA (analysis of variants) was used as a statistical model for the overall evaluation of plant phenotypic characteristics. An F-test was carried out on all the parameters measured of all the plants of all the events transformed with the gene of the present invention. The F-test was carried out to check for an effect of the gene over all the transformation events and to verify for an overall effect of the gene, also known as a global gene effect. The threshold for significance for a true global gene effect was set at a 5% probability level for the F-test. A significant F-test value points to a gene effect, meaning that it is not only the presence or position of the gene that is causing the differences in phenotype.

Since two experiments with overlapping events were carried out, a combined analysis was performed in addition to the analysis described above. This is useful to check consistency of the effects over the two experiments, and if this is the case, to accumulate evidence from both experiments in order to increase confidence in the conclusion. The method used was a mixed-model approach that takes into account the multilevel structure of the data (i.e. experiment-event-segregants). P-values were obtained by comparing likelihood ratio test to chi square distributions.

3.1 Seed-Related Parameter Measurements

The mature primary panicles were harvested, bagged, barcode-labeled and then dried for three days in an oven at 37° C. The panicles were then threshed and all the seeds were collected and counted. The filled husks were separated from the empty ones using an air-blowing device. The empty husks were discarded and the remaining fraction was counted again. The filled husks were weighed on an analytical balance. The number of filled seeds was determined by counting the number of filled husks that remained after the separation step. The total seed yield was measured by weighing all filled husks harvested from a plant. Total seed number per plant was measured by counting the number of husks harvested from a plant. The harvest index in the present invention is defined as the ratio of total seed yield and the aboveground area (mm²) multiplied by a factor 10⁶.

3.2 Aboveground Area

Plant aboveground area was determined by counting the total number of pixels from the pictures from the aboveground plant parts discriminated from the background. This value was averaged for the pictures taken on the same time point from the different angles and was converted to a physical surface value expressed in square mm by calibration. Experiments show that the aboveground plant area measured this way correlates with the biomass of plant

The table of results (Table 5) below shows percentage difference between the transgenics and the corresponding nullizygotes, for harvest index.

The combined analysis performed confirms the consistency of the effects over the two experiments, and thus increases confidence in the conclusion.

TABLE 5 Harvest index Harvest Index P value T1% increase T2% increase combined Event 1 55 24 0.0024 Event 2 35 11 0.0585 Overall 9 (5 events) 8 (4 events) 0.0063 

1. A method for increasing plant yield in plants grown under non-stress conditions relative to yield in corresponding wild type plants grown under comparable conditions, comprising i) introducing and/or expressing in the cytosol of a plant cell a construct comprising an endosperm-specific promoter and an exogenous type I DnaJ-like nucleic acid encoding a type I DnaJ-like polypeptide or a homologue thereof comprising a CaaX motif at its carboxy terminus, and ii) selecting a plant with increased plant yield compared to a corresponding wild type plant.
 2. The method according to claim 1, wherein said type I DnaJ-like nucleic acid is of prokaryotic or eukaryotic origin.
 3. The method according to claim 1, wherein said endosperm-specific promoter is a rice prolamin RP6 promoter.
 4. The method according to claim 1, wherein said increased plant yield is increased seed yield or increased harvest index.
 5. A plant obtained by the method according to claim
 1. 6. A method for the production of a transgenic plant having increased yield, which method comprises: (i) introducing and/or expressing in the cytosol of a plant, plant part or plant cell a construct comprising an endosperm-specific promoter and a nucleic acid encoding a type I DnaJ-like polypeptide or a homologue thereof comprising a CaaX motif at its carboxy terminus; (ii) selecting a plant with increased plant yield compared to a corresponding wild type plant, and (iii) cultivating the plant, plant part or plant cell under non-stress growth conditions promoting plant growth and development.
 7. A transgenic plant having increased yield under non-stress growth conditions resulting from a type I DnaJ-like nucleic acid introduced and/or expressed in said plant, wherein said type I DnaJ-like nucleic acid encodes a type I DnaJ-like polypeptide or a homologue thereof comprising a CaaX motif at its carboxy terminus, and wherein said type I DnaJ-like nucleic acid is operably linked to an endosperm-specific promoter.
 8. The transgenic plant according to claim 7, wherein said plant is a monocotyledonous plant.
 9. Harvestable parts of the transgenic plant according to claim 7, wherein the harvestable parts comprise said type I DnaJ-like nucleic acid operably linked to the endosperm-specific promoter.
 10. Harvestable parts according to claim 9, wherein said harvestable parts are seeds.
 11. The method according to claim 1, wherein said type I DnaJ-like nucleic acid is of plant origin.
 12. The method according to claim 1, wherein said type I DnaJ-like nucleic acid is derived from a monocotyledonous plant.
 13. The method according to claim 12, wherein the monocotyledonous plant is from the family Poaceae.
 14. The method according to claim 12, wherein the monocotyledonous plant is Oryza sativa.
 15. The transgenic plant according to claim 7, wherein said plant is selected from the group consisting of sugarcane, rice, maize, wheat, barley, millet, rye, oats and sorghum.
 16. The transgenic plant according to claim 7, wherein said type I DnaJ-like nucleic acid is of prokaryotic or eukaryotic origin.
 17. The transgenic plant according to claim 7, wherein said type I DnaJ-like nucleic acid is of plant origin.
 18. The transgenic plant according to claim 7, wherein said type I DnaJ-like nucleic acid is derived from a monocotyledonous plant.
 19. The transgenic plant according to claim 18, wherein the monocotyledonous plant is from the family Poaceae.
 20. The transgenic plant according to claim 18, wherein the monocotyledonous plant is Oryza sativa.
 21. The transgenic plant according to claim 7, wherein said endosperm-specific promoter is a rice prolamin RP6 promoter.
 22. The transgenic plant according to claim 7, wherein said increased plant yield is increased seed yield or increased harvest index.
 23. A plant obtained by the method according to claim
 6. 